linux-kernel - Re: [PATCH] s390: Replace zero-length array with flexible-array member

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Date:   Tue, 25 Feb 2020 14:57:12 +0100
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Stefan Haberland <sth@...ux.ibm.com>,
        Jan Hoeppner <hoeppner@...ux.ibm.com>,
        Sebastian Ott <sebott@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390: Replace zero-length array with flexible-array
 member

On Fri, Feb 21, 2020 at 09:06:12AM -0600, Gustavo A. R. Silva wrote:
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
> 
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
> 
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
> 
> This issue was found with the help of Coccinelle.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  arch/s390/appldata/appldata_os.c      | 2 +-
>  drivers/s390/block/dasd_diag.c        | 2 +-
>  drivers/s390/block/dasd_eckd.h        | 2 +-
>  drivers/s390/char/raw3270.h           | 2 +-
>  drivers/s390/char/sclp_pci.c          | 2 +-
>  drivers/s390/cio/idset.c              | 2 +-
>  drivers/s390/crypto/pkey_api.c        | 2 +-
>  drivers/s390/crypto/zcrypt_ccamisc.h  | 2 +-
>  drivers/s390/crypto/zcrypt_msgtype6.c | 2 +-
>  9 files changed, 9 insertions(+), 9 deletions(-)
> 

Applied, thanks